The article “Laser diode self-mixing technique for sensing applications” by G. Giuliani et al., Journal Of Optics A: Pure And Applied Optics, 2002, volume 4, pages 283 to 294, discloses an apparatus for measuring a distance, which uses self-mixing interference (SMI) for determining the distance. A laser comprising a cavity emits a first laser beam, which is directed to an object to which a distance should be determined. The first laser beam is reflected by the object and the reflected laser beam enters the cavity, in which the emitted laser beam and the reflected laser beam interfere. The interference generates an SMI signal, which is measured, while the current for driving the laser is modulated. The modulation of the driving current leads to a wavelength shift of the laser beam and a phase shift of the SMI signal, wherein the distance is determined based on the phase shift of the SMI signal and the wavelength shift.
Since for determining the distance the current for driving the laser has to be modulated, advanced electronics are needed, i.e. the technical efforts required for measuring the distance are relatively high.